Forced-flow once-through vapor generator



Dec. 12, 1967 H. KAMM- 3,357,411

FORCED-FLOW ONCE-THROUGH VAPOR GENERATOR 5 Sheets-Shem 1 B7 /W7Wm Dec. 12, 1967 H. KAMM FORCED-FLOW ONCE'THROUUH VAPOR GENERATOR ,W m R. Mb 0 w MW NM NM ZMW N m 7 MW 0 3 0 2 g Y 2 5 B fi a IV! W k W :v LLLL k W m Dec. 12, 1967 H KAMM 3,357,413

' FORCED FLOW ONCE'THROL'GH VAPOR GENERATOR Filed Sept. 28, 1965 5 Sheets-Sheet C- L L 7 f -3 L A a 4 7 a L Q j INVENTOR. Q fiimar /9/v/-7 United States Patent ABSTRACT OF THE DISCLOSURE A second evaporator is connected to the separator between the first evaporator and superheater of the vapor generator in parallel with the first evaporator. This second evaporator removes a partial flow from the medium delivered to the first evaporator and subjects such to a heat exchange within a superheater of the vapor generator so as to permit a part load operation of the generator.

The invention relates to a forced-flow once-through vapor generator for full-load and for part-load operation, comprising a water separator disposed between the evaporator and the superheater, and comprising a second evaporator.

A forced-flow once-through vapor generator is usually designed for a wide range of capacity and a specific throughput of working medium is fixed for each capacity within the range. When such vapor generators are operated under part-load conditions, unstable flows may occur in the tube system as a result of inadequate quantity of Working medium and may result in damage to the tubes because of excessive tube wall temperatures. To obviate this disadvantage it is conventional practice to protect those tubes of the system under part-load operation by means or" additional circulation of Working medium. In this case the working medium flowing through the tubes in the forced-flow system has an additional circulation of working medium superimposed so that the tubes which are exposed to danger receive a greater quantity of working medium than that intended for part-load operation.

The object of the invention is to provide a forced-flow once-through vapor generator of this type which permits part-load operation without an additional circulation of working medium and without the evaporator tubes being exposed to any danger. Apart from the small quantity of working medium which is removed from the separator together with any impurities, the vapor generator according to the invention is fed only with the amount of Working medium required for vapor generation, and this applies to part-load operation as well.

To this end, according to the invention, the second evaporator which is connected to a bypass pipe branching from a pipe after an economiser and which is disposed in manner known per se in the form of a double tube concentrically inside the superheater tubes is designed approximately for the amount of working medium not required for part-load operation and is adapted to be disconnected.

Instability is thus obviated both under full-load and part-load conditions without the use of a circulating pump in the evaporator, and hence adequate cooling of the evaporator tubes in the radiation section is obtained even under part-load operation of the vapour generator, because the Working medium then flows at adequate speed through the tubes of the radiation evaporator because the second evaporator is disconnected. If the bypass pipe branching off after the economiser is disconnected for a part-load operation so that no working medium flows through the second evaporator disposed inside the superheater tubes, there will not be any damage due to high temperature at the evaporator tubes inside the superheater tubes despite the fact that the flue gases still have the same path, because these tubes are not touched by the flue gases but only by the working medium flowing in the superheater tubes. The evaporator tubes can therefore assume only the temperature of this working medium, and this temperature is safe for the tube material. The second evaporator is thus not heated by the flue gases directly but indirectly as an inner tube after the style of a threeflow heat exchanger. The vapor generator according to the invention also provides satisfactory live steam temperature control even at part-load.

According to one embodiment of the invention, the working medium leaving the second evaporator enters the separator at substantially the same temperature as the working medium leaving the first evaporator. This arrangement ensures a substantially constant temperature of the Working medium entering the following superheater.

According to another embodiment of the invention, the double tube heat exchanger consisting of the superheater and the second evaporator consists of a plurality of parallel-connected heating surface groups disposed at different flue gas temperature zones. The eflect of this arrangement is that the different amounts of heat absorption of the heating surface groups is largely compensated over the entire load range because radiation and contact heating surfaces have opposite characteristics.

These and other objects and advantages of the invention will become more apparent from the following detailed description and appended claims taken in conjunction with the accompanying drawings in which:

FIG. 1 illustrates a schematic view of a vapor generator according to the invention;

FIG. 2 illustrates a schematic view of a modified vapor generator of the invention with a plurality of heating surface groups disposed at different flue gas temperature zones; and

FIG. 3 illustrates a schematic view of another modified vapor generator of the invention with a heat exchanger disposed outside the flow of flue gas.

One exemplified embodiment of the invention is illustrated diagrammatically in FIG. 1 of the drawing. The forced-flow once-through vapor generator according to the invention consists essentially of the evaporators 1 and 2, the superheaters 36 and the water separator 7. The evaporator 1 is heated directly, i.e. by the fire radiation, while the evaporator 2 is heated indirectly. The evaporator 1 which consists of a plurality of tubes connected in parallel extends from an entry distributor 8 to an exit header 9 and is connected via a pipe 19 to the separator 7. The vapor leaving the separator 7 is taken via pipe 11 and a distributor 12 to a superheater 3 which forms a preliminary superheated. The superheater 3 consisting of a plurality of tubes connected in parallel merges into a superheater 4 which together with the evaporator 2 consisting of an equal number of parallel-connected tubes is constructed as a double tube heat exchanger. The superheater 4 is followed by the superheater 5 with the header 13, which is followed by the final superheater 6 with the headers 14 and 15. The live vapor is taken from pipe 16 and fed to a consumer, e.g. a steam turbine. The boiler feed water is fed via a feed pipe 17 by a feed pump 18 to an economiser 19 provided with an entry distributor 20 and an exit header 21. From the latter pipe 22 leads to the entry header 8 of the evaporator 1. A pipe 23 containing a shut-01f valve 27 branches from pipe 22 and is connected via an entry distributor 24 to the evaporator 2 which together with the superheater 4 forms the double tube heat exchanger. The evaporator 2 is also connected to the separator '7 via an exit header 25 and a pipe 26. The forced-flow once-through vapor generator according to the invention operates as follows:

The evaporator 2 disposed inside the superheater tubes 4 is designed for that portion of the flow of working medium which is not required for part-load operation. Durpart-load operation the valve 27 in pipe 23 is closed so that the working medium does not flow through the evaporator 2 and the entire quantity of working medium passes solely through the evaporator 1. Thus, there is always an adequate flow of working medium through the evaporator 1 so that satisfactory cooling of the evaporator tubes 1 is guaranteed at all times and no instability occurs. This step is readily admissible because the material from which the tubes of the evaporator 2 are made can assume only the temperature of the heated vapor flowing in the superheated 4. This temperature is safe for the tube material of the evaporator 2.

For a full-load operation the evaporator 1 and the evaporator 2 have the working medium flowing through them in parallel, after which the two component flows enter the separator 7 via the exit headers 9 and 25 respectively and the pipes and 26 respectively. The evaporators 1 and 2 are so designed and arranged that the two component flows enter the separator 7 at substantially the same temperature. The advantage of this arrangement is that the working medium entering the superheater 3 always has the same temperature.

The invention is not restricted to the exemplary embodiments illustrated. For example, the invention may be applied to vapor generators without a separator and/ or with superheated groups connected in a different way.

Referring to FIG. 2, since the modified vapor generator is similar to the above, like reference characters are used to designate like components. A pair of pipes 23, 23 each containing a shut-off valve 27, 27 branch from pipe 22 and are connected via entry distributors 24, 24' to respective evaporators 2, 2' which together with the superheaters 4, 4 form a pair of heating surface groups of the heat exchanger. The evaporators 2, 2' are also connected to the separator 7 via exit headers 25,

and a pipe 26. The operation of this vapor generator is.

similar to the vapor generator described above.

Referring to FIG. 3, a modified vapor generator which is similar to the vapor generator shown in FIG. 1 such that like reference characters are used for like parts has a heat exchanger disposed outside the flow of flue gas. That is, with an economiser 19 disposed on one side of a wall in the flow of flue gas, the exit header 21 is disposed on the opposite side of the wall 30. Pipe 22 leads from the exit header 21 to the entry header 8 of the evaporator 1 disposed in the flow of flue gas. The separator 7 disposed outside the flow of flue gas is connected via pipe 10 to the exit header 9 of the economiser 19 and to the distributor 12 via pipe 11 for transferring the vapor leaving the separator to a superheater 3 in the flow of flue gas. The superheater 3 connects with a header 13 which is followed by a heat exchanger tube 31 outside the flow of flue gas. The tube 31 connects with a header 14 which is followed by a final superheater 6. A pipe 23 containing a shut-off valve 27 branches from pipe 22 and is connected to the evaporator 2 which together with tube 31 forms a double tube heat exchanger. The evaporator 2 is also connected to the separator 7 via pipe 26. The operation of this modified vapor generator is similar to the above operation of the vapor generator of FIG. 1.

What is claimed is:

1. A fume-gas heated forced-flow once-through vapor generator for full load and part load operation comprismg a working medium feed means,

an economiser connected to said feed means for receiving working medium directly therefrom,

a first evaporator means connected to said economiser for receiving a first portion of the working medium directly therefrom for part load operation,

a separator means connected to said first evaporator for receiving said first portion of the working medium therefrom,

a plurality of superheater means for receiving a working medium from said separator means,

a second evaporator means positioned within one of said superheater means forming a heat exchanger therewith,

valve means interposed between said economiser and said second evaporator for directing a second portion of the working medium into said second evaporator, and

means connecting said second evaporator means to said separator means whereby said second portion of the working medium is passed through said second evaporator means and direct to said separator.

2. A vapor generator as set forth in claim l wherein said heat exchanger includes a plurality of parallel-connected heating surface groups disposed at different flue gas temperature zones.

3. A vapor generator as set forth in claim 1 wherein said heat exchanger is disposed outside the flow of flue gas.

References Cited UNITED STATES PATENTS 2,966,896 1/1961 Vogler l22479 X 3,035,556 5/1962 Brunner 122479 X 3,186,175 6/ 1965 Strohmeyer 122479 X FOREIGN PATENTS 967,022 8/1964 Great Britain.

CHARLES J. MYHRE, Primary Examiner. 

1. A FUME-GAS HEATED FORCED-FLOW ONCE-THROUGH VAPOR GENERTOR FOR FULL LOAD AND PART LOAD OPERATION COMPRISING A WORKING MEDIUM FEED MEANS, AN ECONOMISER CONNECTED TO SAID FEED MEANS FOR RECEIVING WORKING MEDIUM DIRECTLY THEREFROM, A FIRST EVAPORATOR MEANS CONNECTED TO SAID ECONOMISER FOR RECEIVING A FIRST PORTION OF THE WORKING MEDIUM DIRECTLY THEREFROM FOR PART LOAD OPERATION, A SEPARATOR MEANS CONNECTED TO SAID FIRST EVAPORATOR FOR RECEIVING SAID FIRST PORTION OF THE WORKING MEDIUM THEREFROM, A PLURALITY OF SUPERHEATER MEANS FOR RECEIVING A WORKING MEDIUM FROM SAID SEPARATOR MEANS, A SECOND EVAPORATOR MEANS POSITIONED WITHIN ONE OF SAID SUPERHEATER MEANS FORMING A HEAT EXCHANGER THEREWITH, VALVE MEANS INTERPOSED BETWEEN SAID ECONOMISER AND SAID SECOND EVAPORATOR FOR DIRECTING A SECOND PORTION OF THE WORKING MEDIUM INTO SAID SECOND EVAPORATOR, AND MEANS CONNECTING SAID SECOND EVAPORATOR MEANS TO SAID SEPARATOR MEANS WHEREBY SAID SECOND PORTION OF THE WORKING MEDIUM IS PASSED THROUGH SAID SECOND EVAPORATOR MEANS AND DIRECT TO SAID SEPARATOR. 